Generally, in metal joints in electrical and electronic devices, solder joints using solder pastes are used, and for such a solder paste, conventionally, a solder alloy containing lead is used.
However, recently, it has been required to suppress lead usage in view of environmental burden, and therefore a solder alloy (lead-free solder alloy) containing no lead is under development.
For such a lead-free solder alloy, for example, a tin-copper alloy, a tin-silver-copper alloy, a tin-bismuth alloy, and a tin-zinc alloy have been well-known, and in particular, a tin-silver-copper alloy has been widely used because of its excellent strength.
Meanwhile, silver contained in tin-silver-copper alloys is very expensive, and therefore reduction in the silver content has been required in view of cost reduction. However, simply reducing the silver content may cause poor fatigue resistance (particularly cold thermal fatigue) and poor connection.
Furthermore, such a tin-silver-copper alloy has been required to have well-balanced strength and extensibility, and at the same time have a suitable melting point.
To meet such requirements, Patent Document 1 below has proposed, as a tin-silver-copper alloy with a reduced silver content, to be specific, a low silver solder alloy consisting of, for example, 0.05 to 2.0 mass % of silver, 1.0 mass % or less of copper, 3.0 mass % or less of antimony, 2.0 mass % or less of bismuth, 4.0 mass % or less of indium, 0.2 mass % or less of nickel, 0.1 mass % or less of germanium, 0.5 mass % or less of cobalt, and a remaining mass % of tin.